In the molding of certain plastic articles, hingedly connected upper and lower mold members are clamped in a closed position during a molding operation and are released and swung apart at the conclusion of the operation to allow the molded part to be removed from the lower mold member. Various devices are known that enable releasable clamping force to be manually applied to mold members, but the clamping devices heretofore available for the purpose have not been accommodated to a problem that arises with plastics that have a tendency to adhere to mold surfaces. Foam plastics particularly exhibit this tendency, even when releasing agents are used with them. When such materials are molded adhesion between the molded article and the upper mold member resists separation of the mold members.
Prior manually operated mold clamping mechanisms made no provision for forceful separation of the mold members against such adhesion. Hence, mold operators had to exert great force on the clamping mechanism handle in order to break the adhesion between the upper mold member and the molded article, or resorted to various time consuming improvisations for forcing the upper mold member away from the lower one.
Power driven actuators can of course apply clamping and releasing forces of substantial magnitude, but powered actuators are relatively expensive, especially if they are complicated, as in the case of the molding apparatus disclosed in U.S. Pat. No. 3,816,052. A less complicated powered mechanism for bringing upper and lower mold members into clamped engagement and for separating them at the conclusion of a molding operation is disclosed in the U.S. Pat. No. 4,080,145 to Jung. However, even the mechanism of the last mentioned patent incorporates two pressure fluid energized cylinder jacks, one of them for moving the upper mold member vertically to and from engagement with the lower member and the other one for swinging the upper member to a position in which the lower mold member is accessible for removal of a molded part therefrom.
For many molding operations the cost of even a simple power mechanism is not economically justified; but, on the other hand, production tends to be delayed by the need for exerting high manual forces for mold opening, and there is a further element of cost in the unpleasant working conditions created by that necessity. It has long been obvious that there was inconvenience and inefficiency in manually operated mold clamps that could not effect forceful separation of the mold members along with the release of clamping force, but heretofore no mechanism was available which could be operated to accomplish that objective, notwithstanding the very evident need for it.
To be satisfactory, such a manually operated device should have a single actuator and should be so arranged that a single convenient and natural movement of that actuator first releases clamping force on the mold members and then forces the upper mold member upwardly away from the lower one without the need for exerting any great manual effort. Once the mold members are initially separated, it should be possible to use the same actuator as a handle whereby the upper mold member can be swung about its hinged connection with the lower one to fully open the mold so that the molded article can be removed from the lower mold member. Inasmuch as the cooperating parts of the clamping device that are mounted on the upper and lower mold members, respectively, are separated by a substantial distance when the upper mold member is swung to its fully open position, those parts should be brought directly back into cooperating relationship with one another as the upper mold member is swung back towards its mold closed position, so that the mold can be clamped shut quickly and conveniently.
The present invention meets all of these requirements.